This invention relates to electric circuits and methods for supplying control voltage to tunable dielectric devices, and more particularly to such circuits that can rapidly adjust the supplied voltage.
Tunable dielectric materials are materials whose permittivity (more commonly called dielectric constant) can be varied by varying the strength of an electric field to which the materials are subjected. Even though these materials work in their paraelectric phase above the Curie temperature, they are conveniently called xe2x80x9cferroelectricxe2x80x9d because they exhibit spontaneous polarization at temperatures below the Curie temperature. Tunable ferroelectric materials including barium-strontium titanate (BST) or BST composites have been the subject of several patents.
Tunable dielectric materials are recently receiving increased attention due to performance breakthroughs that overcome prior limitations. As a result of such breakthroughs, many commercially viable applications involving tunable dielectric materials are now imminent.
Current applications utilizing tunable materials vary widely and include scanning antennas for both point-to-multi-point and point-to-point applications. Also included are a wide range of tunable filter applications, voltage controlled oscillator applications, and delay line applications, as well as other applications including low cost frequency tunable patch antennas.
This has given rise to a need for low cost circuitry capable of providing a digitally controllable bias voltage to drive these tunable components. Such circuitry is typically referred to as a high voltage driver or as a high voltage switcher. Components based on tunable dielectric materials will typically require drive voltages ranging from tens of volts up to thousands of volts, with most commercially viable applications currently requiring hundreds of volts. Technology trends are toward lower drive voltages.
Tunable dielectric materials have several inherent advantages including sub-nanosecond response times and very low current draw under switching conditions. Low current draw translates into low power consumption by the tunable material. A low cost driver circuit that does not compromise these inherent advantages of the tunable dielectric materials would be highly desirable.
This invention provides a circuit for providing a control voltage for tunable dielectric devices, the circuit comprises an input for receiving a voltage command signal, a charging circuit for establishing a desired voltage level on a first capacitor in response to the voltage -command signal, and a switch for switching voltage on the first capacitor to a tunable dielectric device to control a dielectric constant of tunable dielectric material in the tunable dielectric device. A second capacitor, second charging circuit, and second switch can be used to provide voltage to the tunable dielectric device during charging or discharging of the first capacitor.
The invention also encompasses circuits for providing a control voltage for tunable dielectric devices, wherein the circuits comprise means for receiving a voltage command signal, means for establishing a desired voltage level on a first capacitor in response to the voltage command signal, and means for switching voltage on the first capacitor to a tunable dielectric device to control a dielectric constant of tunable dielectric material in the tunable dielectric device. A second capacitor, means for charging the second capacitor, and means for switching voltage on the second capacitor to a tunable dielectric device can be used to provide voltage to the tunable dielectric device during charging or discharging of the first capacitor.
The invention further encompasses a method for providing a control voltage for tunable dielectric devices, the method comprising the steps of receiving a voltage command signal, establishing a desired voltage level on a first capacitor in response to the voltage command signal, and switching voltage on the first capacitor to a tunable dielectric device to control a dielectric constant of tunable dielectric material in the tunable dielectric device. The method can further include the steps of establishing a desired voltage level on a second capacitor in response to the voltage command signal, and switching voltage on the second capacitor to the tunable dielectric device to control the dielectric constant of the tunable dielectric material in the tunable dielectric device.
The circuits and method of this invention can be used to control the dielectric constant of tunable dielectric materials in a variety of devices to provided rapid changes in the dielectric constant of the tunable materials, and therefore rapid changes in the performance characteristics of the tunable dielectric devices.